Standard ATX power supplies aren't designed to turn on unless they are properly connected to a motherboard. This helps to ensure that they can't power up and damage computer components if the plug isn't fully connected or connected the right way. However, if you're looking to test components, want to put a large number of hard drives in a case to expand your office server's capacity, or need more power to cool a financial modeling workstation, there is a way to use a computer power supply when you don't have the motherboard installed. All that you need is some wire and a single-pole switch that stays on or off when you flip it or press its button -- an inexpensive light switch is fine unless you want something more aesthetically pleasing or easier to mount.

Cut two lengths of wire that will be long enough to connect to your switch and to the 20-pin power connector coming off of your power supply.

Strip the insulation off of one end of each wire, leaving enough wire to wrap around your switch's terminal. On the other end, strip just enough wire to go into the much-smaller terminals on your power supply's 20- or 24-pin motherboard connector.

Loosen the screw on one of your switch's terminals, wrap the longer end of bare wire around it and use your screwdriver to re-tighten the terminal. Repeat the process with the other wire and the other terminal. Set the switch to the "Off" position.

Unplug your computer's power supply from the wall.

Hold your power supply's 20- or 24-pin motherboard-connection plug with the terminals facing you and the plastic locking piece facing upward and the flat edge facing downward.

Insert one wire from the switch in the third terminal on the top row. There should be two empty terminals to its left. Insert the other wire into the terminal directly to the right of the first wire. You should have two empty terminals, two terminals with a wire in them, then six or eight empty terminals, depending on if it is a 20- or 24-pin connector to the right of them. The bottom row should be empty.

Plug the power supply back into the wall and turn its power switch on, if it has one.

Set the switch that you just installed to the "On" position. The power supply will turn on and you can now use it to power devices or for testing purposes.

Things Needed

Switch

Wire

Wirecutter

Screwdriver

Tips

Once the wires from the switch are connected to the power supply and you have confirmed that everything is working, you can solder them in place or use electrical tape to secure them for a more permanent solution.

You can also permanently leave your power supply on by running a single wire between the two terminals.

Warning

Do not work with your power supply while it is plugged into the wall. You could damage your power supply, damage other connected components or be electrocuted.

About the Author

Steve Lander has been a writer since 1996, with experience in the fields of financial services, real estate and technology. His work has appeared in trade publications such as the "Minnesota Real Estate Journal" and "Minnesota Multi-Housing Association Advocate." Lander holds a Bachelor of Arts in political science from Columbia University.